Dispersions of coal in oil



Patented Dec. 12, 193.3

UNETED ST EN oFFic 1,939,587 nrsraasrons or COAL n on.

Robert Andrew Adam,

Waterloo, Frederick Charles Victor Holmes, Bromborough, and Arthur Wright Perrins, Bebington, England, as-

signors to The Cunard Steam Ship Company No. 618,806, and in 1931 9 Claims.

This invention relates to improvements in the production of stable dispersions of coal in oil.

It has already been proposed to disintegrate coal in oil until the suspended particles are reduced to colloidal fineness. It has also been proposed to prepare relatively coarse dispersions of coal stabilized in oil by the aid of a fixature or peptizers or by other measures.

The cost of grinding to colloidal dimensions is 10 heavy. If, however. the usual stabilized coarse dispersions are heated, their stability is reduced.

In spite of the elaborate measures which have previously been proposed it is believed that stable dispersions of coal in oil have not found the expected success in industry and our experiments lead to the conclusion that in large scale operation there has often been a danger of separation of solid particles.

The primary object of the present invention is to provide a process in which practically unlimited stability is secured ina cheap way. We have made the very surprising discovery that the elaborate measures previously considered necessary need not be employed provided that both the oil 5 and the coal are caused to comply with certain very simple requirements. The scope of the invention is defined in the appended claims, but it will be noted that according to the invention it is possible to make suspensions of practically unlimited stability without the use of any added stabilizing agent and without any unusual treatment of the mixture of solid and liquid.

The present invention consists in a process in which stable dispersions are made by using coal which has been finely ground by mechanical means in conjunction with oil which has been specially selected or treated so as to possess the relevent properties of cracked oils, that is, fuel oil resulting from the cracking process, and commonly known and hereafter described as cracked oil. Thus cracked oils themselves may be used or other oils such as straight-run fuel oils may be blended with cracked oils or otherwise treated so that they behave in a similar manner.

In one form of the invention the percentage of fixed carbon" is used as a criterion of suitability.

The coal must be finely ground and in one form of the invention it may be so fine that practically nothing is left on a 200 mesh sieve (200 strands per linear inch). If the mill only reduces to a size such that 95% passes the 200 mesh sieve. the 5% over-size may be eliminated by classification. Numerous recognized methods are available for this purpose. Normally the over-size is re- Great Britain November 2,

jected prior to admixture with the oil in the mill, but in some cases. e. g. when using a disc bar mill to homogenize the powdered coal and oil it is possible to reject say 5% over-size in the disc bar mill itself.

We prefer a coal of which 100% passes a 200 mesh sieve I.M.M.). It is important to exclude even a small proportion of really coarse particles which cause trouble in various ways. Results can however be obtained if all the powder passes "a slightly coarser sieve e. g. 180 mesh; the size of the coarsest particles must be limited.

We have found that good results are obtained by using a cracked fuel oil, but oils of similar properties may be substituted. One way of doing this is to treat an oil which is normally unsuitable e. g. a straight-run fuel oil by increasing its fixed carbon" content for example by blending with a cracked fuel oil or with a suitable liquid product of distillation such as coal tar. We may also use oil so treated in distillation or other processes as to be equivalent to cracked fuel oil in its stabilizing properties.

For practical purposes about 6% of fixed carbon" appearsto be near the critical limit but this limit depends upon the relative proportion of coal and oil.

The following illustrative example indicates results which have been obtained but the invention is not limited to these data especally as regards fixed carbon" percentage in the oil or fineness of grinding of the coal:-

. Example Take 40 parts by weight of an average steam coal (about 5% ash) ground dry so that the whole passes through a sieve of 200 meshes per linear inch. Mix this powder with parts by weight of a cracked fuel oil having the following characteristics: 85

High content of free carbon. Specific gravity 0.98. Flash point (closed Pensky Martin 200-225 F.) Viscosity in Saybolt furol units: mo

12-16 at 225 F. 25-30 at 175 F. 55-90 at 122 F.

We have found that when coal of specified fineness is intimately mixed with various fuel oils, in some cases a stable mixture results whilst in others the coal settles out. For example. when 60 parts of a fuel oil of "fixed carbon" 3.1% is mixed with 40 parts of 200-mesh screened coal the coal gradually separates out on standing, the

more readily when the mixture is heated. If oil of fixed carbon 8.9% is mixed in the same proportions with similar pulverized coal a stable mixture results which does not show settling even when heated for considerable periods.

We have also found that when 30 parts of each of the above oils are intimately mixed with 40 parts of pulverized coal of the requisite fineness a stable mixture is again formed. On the other hand, a preponderance of the oil whose fixed carbon is 3.1% produces an unstable mixture.

In selecting coal for use according to the present invention we prefer a bituminous or somewhat bituminous coal of reasonably low ash content but satisfactory results have been obtained with coal of high ash content.

In selecting or preparing the oil fixed carbon may be determined as follows:

1 gram of the fuel is strongly heated for 7 minutes over a Bunsen flame 20 cms. high in a fused silica crucible 35 mm. deep, 20 mms. wide at bottom and 40 mms. wide at top, the bottom of the crucible being 6 to 8 cms. from the top of the burner. The crucible is provided with a loosely-fitting porcelain lid. After heating, the contents are allowed to cool and then Weighed. The residue left in the crucible represents the fixed carbon content.

The method of incorporation is as follows:

The coal is pulverized and classified so that all passes through a 200 mesh sieve. After rough mixing in a warm mixing bath, the coal and oil mixture is passed through a homogenizer which may be of any usual form provided a reasonably intimate mixing results.

The fuel has been pumped and handled by the usual oil fuel burning equipment. It may be necessary to heat the fuel so as to reduce its viscosity for convenience of transfer.

We declare that what we claim is:

1. The method of preparing a stable dispersion of coal and fuel oil which consists in mixing coal pulverized finely but not disintegrated to colloidal fineness into a fuel oil containing at least six percent of fixed carbon, so that an inherently stable liquid fuel is obtained.

2. The method of preparing a stable dispersion of coal in a combustible oil liquid medium, which comprises finely pulverizing coal without disintegrating it wholly to colloidal fineness, intimately mixing it with an oil comprised principally of a fuel oil and containing not less than about six percent of fixed carbon, and at some stage rejecting all particles substantially greater than 200 mesh.

3. The method of preparing a stable dispersion of coal in a fuel oil, which comprises finelypulverizing coal but not disintegrating it wholly to colloidal fineness, mixing "it with a cracked fuel oil containing not less than six percent of fixed carbon, and at some stage rejecting all particles substantially greater than 200 mesh.

4. The method of preparing a stable dispersion of coal in a combustible oil medium, which consists in introducing coal pulverized finely but not disintegrated to colloidal fineness into an oil comprised principally of a fuel oil and containing at least six percent of fixed carbon, and homogenizing the mixture, and at some stage rejecting all particles substantially greater than 200 mesh.

5. A stable liquid fuel whose stability is substantially unaffected by the presence of water and which can endure heating during preparation for burning, consisting of a large proportion of coal finely pulverized but not disintegrated to colloidal fineness, dispersed in a hydrocarbon oil containing not less than about six percent of fixed carbon so that the said hydrocarbon oil is self-sufficient for stability in the absence of an added stabilizer and comprised at least in principal part of a fuel oil.

6. A stable liquid fuel'whose stability is substantially unaffected by the presence of water and which can endure heating during preparation for burning, consisting of a large proportion of pulverized coal containing no particles substantially greater than 200 mesh but not disintegrated to colloidal fineness, dispersed in an (11 containing not less than about six percent of fixed carbon so that it isself-sufficient for stability and comprised at least in principal part of a fuel oil.

7. A stable liquid fuel whose stability is substantially unafiected by the presence of water and which can endure heating during preparation for burning, consisting of a large proportion of pulverized coal containing no particles substantially greater than 200 mesh but not disintegrated to colloidal fineness, dispersed in a mixture of hydrocarbon oil and tar, said mixture containing not less than about six percent of fixed carbon so that it is self-sufficient for stability in the absence of an added stabilizer and comprised in principal part of a fuel oil.

8. A stable liquid fuel whose stability is substantially unaffected by the presence of water and which can endure heating during preparation for burning, consisting of a large proportion of pulverized coal containing no particles substantially greater than 200 mesh but not disintegrated to colloidal fineness, dispersed in a cracked fuel oil containing not less than about six percent of fixed carbon so that it is selfsuificient for stability in the absence of an added stabilizer.

9. A stable liquid fuel whose stability is substantially unaffected by the presence of water and which can endure heating during preparation for burning, consisting of about forty percent by weight of pulverized coal containing no particles greater than 180 mesh but not disintegrated to colloidal fineness, dispersed in an oil containing not less than about six percent of fixed carbon so that it is self-sufficient for stability and comprised at least in principal part of 9 a fuel oil.

ROBERT ANDREW ADAM. FREDERICK CHARLES VICTOR HOLMES. ARTHUR WRIGHT PERRINS. 

